PHYTOPATHOLOGY/MYCOLOGY ABSTRACTS OF PRESENTATIONS AT THE 25TH CONGRESS OF THE ISRAELI PHYTOPATHOLOGICAL SOCIETY February 23-24, 2004 ARO, The Volcani Center, Bet Dagan, Israel A: CHARACTERIZATION OF PATHOGENS AND PATHOGENESIS pthG from Pantoea agglomerans pv. gypsophilae Encodes an Avirulence Effector that Determines Incompatibility in Multiple Beet Species D.M. Weinthal, 1,2 D. Ezra, 1 I. Barash, 2 V. Gaba 3 and S. Manulis 1,* 1Dept. of Plant Pathology and Weed Research and 3Dept. of Virology, ARO, The Volcani Center, Bet Dagan 50250 [*e-mail: shulam@volcani.agri.gov.il]; and 2Dept. of Plant Sciences, TeloAviv University, Tel Aviv 69978, Israel Pamoea agglomerans pv. gypsophilae (Pag) causes root and crown gall disease on gypsophila, whereas P agglomerans pv. betae (Pab) induces the disease on beet as well as gypsophila. Both pathovars harbor a pathogenicity pIasmid (pPATHp,~g or pPATHp,~b) that determines disease development. We have previously isolated and partially characterized a pleiotropic gene from the pPATHpa9 designated as pthG that encodes a virulence factor in gypsophila and an elicitor of a hypersensitive-like response in beet roots. The present study was undertaken to characterize pthG further as an avr gene. Infiltration of beet leaves with strains expressing PthG (i.e., Pag or Pab containing pthG in trans) caused an HR response within 48 h, whereas strains lacking intact pthG (i.e., Pab or Pag mutated in pthG) resulted in gall formation after 5 days. HR was elicited by pthG on multiple beet species, whereas a marker exchange mutant of Pag in pthG extended its host range on these beet species. A marker exchange mutant of Pag in hrpJ, encoding a component of the Type III secretion system, prevented HR el icitation. Mutations in each of the hrp regulatory genes (hrp Y, hrpS and hrpL) substantially reduced the transcriptional activity ofpthG in gypsophila cuttings. Panicle bombardment of GFP-PthG fusion caused cell death in beet but not in non-host (melon) leaves. Present and previous results have established pthG as a broad-host-range avr gene that functions in multiple host plant species and the first functional avr gene in Pantoea spp. These characteristics of pthG may be utilized for creating resistant beet plants against several pathogens. [L] Anatomical Changes Involved in Gall Formation Caused by Pantoea agglomerans pv. gypsophilae on Gypsophila paniculata L. Chalupowicz, 1,2 M. Schwartz, 2 R. Aloni, z I. Barash 2 and S. Manulis 1'* 1Dept. of Plant Pathology and Weed Research, ARO, The Volcani Center, Bet Dagan 50250 [*e-mail: shulam @ volcani.agri.gov.il]; and ~ Dept. of Plant Sciences, Tel-Aviv University, Tel Aviv 69978, Israel L = lecture sessions;P = poster (market place) sessions. Phytoparasitica 32:2, 2004 185